Servo mechanism of the hydraulic type



- Nuv.. y 'A. FRAzER-N'AYSH 2,361,934

sERvomEcHANIsM QF THE HYDRAULIC TYPE File lay 7.. 1942 L?" ,ffl

Patented Nov. 7, 1944 SERVO' MECHANISM OF THE HYDRAULIC l t. f i' -TYPE Archibald Goodman Frazer-Nash, lTolvvortli,"England -r Application May 7, 1942, Serial No. 442,115 A i In GreatBritain September 13, 1935 Claims.y `(el. 13s-31') `This invention relates to servo-mechanism1` of` the hydraulic type and particularlyrto servo' mechanism fthetype in question` employed vin aircraft, particularly aeroplanes and also other vehicles, for instance, in connection with mountings forguns and otherinstruments.

In servo-mechanismlof the kind in question it is desirable to provide means whereby the liquid passing-to the suction'side of the pump Vor engine is` maintained under Vslight pressure in order vto prevent cavitation, and" further, to ensurey that any variation in volume "of liquid in circulation in the system is compensated for, and in particular to ensure that the quantity of. oil in circulations adequate. V

It is also desirable to arrange that air Which may have accumulated in the system maybe expelled'when necessary. l

The invention consists', broadly, in servornechani'sm ofth'e hydraulic type in which in the return or exhaust side of the servo-mechanism, that is to say. in the conduit or conduits leading the pressure 'liquid'from' the motor or motors actuated thereby to'the pump or engineby which the pressure liquid is set in motion, there is insei-ted or included a recuperator comprising two chambers arranged one belowY the other and in the lower of Which,"namely, that from which the pressure liquid may be delivered to the pump or engine, is located a spring or similarly loaded'ram or plunger and ports or a valve'controlledby the movementof the plunger to permit 4the pressure liquid to pass, when the volume of liquid in the` chamber has reached alparticular magnitude, yto theupper chamberfiom which, inl turn, theliquid maybe withdrawn by an auxiliary pump and supplied to the first-mentioned ch'arnber.

Thus, for instance, in accordance with the invention, the ramer plunger of the recuperator may be arranged to co-op'erate` with' ports, provided in the wall ofthe chamber in which it is located, or actuate` a lvalve to permit or prevent the passage of the liquid under pressure therefrom to the other chamber.

In one construction, in, accordance with the invention, the ram or plunger is furnished with a rod or the like extending through a passage located within the upper chamber and furnished with apertures ator adjacent to its upper end permitting the pressure -fluid accumulating behind` the plunger to be discharged into the upper chamber from which it may be withdrawn by means of a pump and introduced into the chamber 'in which the ram or plunger isI located, and

inthe Walls of the last-mentioned chamber there are provided ports, spaced apart, and connected together by afpassage sopositioned that when the plunger has been raised to a givenheight,

bythe liquid accumulating below the lower face of the` ramfor plunger, the liquid may be bypassedfrom below thev lowerto the space above therupper faceof the ram or plunger andthus to the passage within which `the rod extending from the plunger is located and from thence to the portion of the upper chamber surrounding the passage.

Conveniently, in` accordance with the invention, the rod` is arranged to extend through the upper end of the passage and it may be furnished with graduations permitting the pressure in the system or, alternativelyJ the volume `of liquid contained in the chamber in which the plunger is located tobe determined.

The pump associated with the device for introducing the liquid from the` upper chamber into the lower chamber in advance of the ram or plunger 'may befurnished with a hand lever or other suitable form of actuating mechanism adapted to be normally locked in an inoperative positionpr in` addition, or alternatively, the lever or equivalent mechanismwhereby the pump is actuated may be connected with some portion of the servo-mechanism to ensure or assist in ensuring that by theactuating of such mechanism the appropriate volume of oil is` contained in the chamber in which the piston or ram is located. The chamber inwh'ichthe ram or plunger is located may be furnished with a blow-off valve adapted to permit, should the pressure in the chamber exceed a predetermined maximum, passage of "liquid therefrom to the other chamber from which, as occasion may arise, the liquid may `be reintroduced into the first-mentioned chamber at a point in advance of the ram or plunger. l

The invention will be described' further in detail and by `way of example with reference to the accompanying drawing, in which:

Figure l is a View in elevationpartly in section of a recuperator, and n n Figure 2 is a similar View with the device rotated through an angle of n Referring to Figures 1 and 2, lis a section of tube in screw-threaded engagement with a base 2 and an upper end element 3.. Within the tube l isarranged a cup Washer 4 located between a lockingk ring 5 and a spreader washer 6 both of which. are in screw-threaded engagement with one end oi the tube 1 the other end of which is in screw-tlneaded engagement at 8 with the upper end element 3, the cup washer and its associated washers dividing the space within the tube into two chambers 9 and I0. i

Within the chamber 9 there is arranged a plunger comprising a cup washer II secured between a piston head I2 and a spreader washer I3 n with which is associated a locking ring I4 engaging an extension I5 on the piston head which is secured by the pin I6 with the piston rod I1 furnished with an end cap I8 and also secured with the sleeve I9 engaging about a portion of the head and about the annulus 28 to form a guide for a spring 2l the lower end of which bears on the piston, the upper end engaging against the cap 22 through which the piston rod passes, a gland nut 23 and a washer 24 being provided for securing a fluid tight joint between the rod and the end element 3.

In the extension on the piston head there are provided slots 25 in which are freely engaged the ends of a cotter 26 passing through the stem of the valve element 21 with which is associated a spring 28, the valve element in question being arranged to co-operate with a seating 29 above or behind which passages 30 and 3I are provided for permitting the pressure liquid to pass from the space below the lower face of the piston to the space above or behind the piston when the body of liquid accumulating in 9 is sufficient to force the piston upward in opposition to the spring 2| into the position shown in Figure 1, in which the cotter 26 extending through the stem of the valve element 21 engaging against the locking ring 5 raises the valve from its seating.

The pressure liquid accumulating in the space above the piston will enter the passage 32 which is located within the chamber IU through which extends the piston rod I1 and which adjacent to its upper end is furnished with apertures 33 adapted to permit the pressure uid accumulating above the piston to be discharged into the chamber I0, the level of the liquid so accumulating being capable of being determined by means of the dip stick 34 the handle 35 of which is provided with an externally screw-threaded portion 36 engaging in an internally screw-threaded aperture 31 in the upper end element 3.

Ihe liquid accumulating in the chamber or introduced into the chamber from an external source should occasion require on the removal of the lling plug 38 is adapted to be withdrawn therefrom by way of the passage 39 on the actuation of the piston 40 furnished with a ball valve 4I and spring 42, the rod 43 of the piston extending through the gland nut 44 and washer 45 engaged in the head 46 off a cylinder 41 in the base of which is provided a chamber 48 in which is located a ball valve 49 and a spring 50 associated therewith. This chamber is furnished with a tubulure 5I with which one end of a pipe 52 is connected, the other end of the pipe being con nected with a tubulure 53 opening into the base of the chamber 9.

In the base of the chamber there are also provided unions 54, 55 for connection with respectively the suction and the delivery side of the pump or engine and unions 56 and 51 for connection to and from the master valve which controls the supply of working fluid to the several motors of the servo-mechanism with which the recuperator is associated. A- non-return valve comprising a movable Valve element 58 and its associated spring 59 located in a chamber 60 iS provided in the connection 55a from the union 55 for permitting the pressure liquid should the pressure in the system rise sullciently to displace the valve from its seating and to pass by way of the passage 55e into the chamber 9.

Normally, however, the valve in question will operate to preclude the passage of the pressure liquid into the chamber, the, pressure liquid normally passing from the passage 55a to the passage 55D and thence through the pipe 51a associated with the union 51 to the pilot valve.

The return from the pilot valve is connected by way of the pipe 56a to the passage 56h which communicates by way of the passage 56e with the chamber 9.

In the construction described above the piston of the pump 41 is arranged to be hand actuated. Instead of such hand actuation any convenient connection may be provided whereby the piston may be actuated at appropriate times as the result of the motion eiected by the servo-actuated mechanism.

In a servo-mechanism in accordance with the invention the quantity of liquid initially introduced into the system and normally maintained therein will be such as at least in part to ll the lower chamber of the recuperator and this body of liquid will thus form a reserve so that should any loss of liquid in circulation arise in the operation of the mechanism, it will be compensated for from the reserve in the recuperator chamber.

When the appropriate quantity of liquid is contained in the recuperator chamber, or in other words in the system, the piston rod I1 will extend to a greater or less distance above the upper chamber, thus indicating the volume of the liquid contained in the lower chamber. Should from any cause the quantity of liquid in the system decrease below a given limit, a further quantity of liquid may be introduced into the system by removing the filler cap 38, introducing liquid into the upper chamber, and thereafter pumping it by means of the auxiliary pump from the upper into the lower chamber from which in turn it will be vsupplied as required to the pump or engine. l

Furthermore, as the lower chamber is arranged to discharge liquid into the upper chamber through openings 33 provided near the upper extremity of the tube 34, any air which may be in the system willtend to accumulate in the top part of this chamber and may be displaced by the introduction into it of a further quantity of liquid.

In conclusion it may be pointed out that a recuperator in accordance with the invention, does not function as an accumulator such as is commonly provided in hydraulic systems in that it does not provide a chamber in which a piston or ram element is arranged and into which chamber a body of liquid under high pressure may be.

stored to meet variations in demand upon the lpump or the engine as in a construction described in the United States Specification No."

1,861,154, but it functions as a reservoir for pressure liquid which is delivered to the pump or engine at a relatively low pressure.

I claim:

1. Recuperator apparatus adapted for use with servo-mechanism of the hydraulic type comprising, in combination with a pressure liquid rewhich said pressure liquid is exhausted, an upper chamber connected with said lower chamber by a. liquid passage independent; of the passage by which said pressure liquid is exhausted as aforesaid, a loaded plunger in said lower chamber which is elevated in response to accumulation of liquid therein, valve means for said passage controlled by movement of said plunger and adapted to be opened when the Volume of liquid in said lower chamber reaches a particular magnitude, whereby said liquid passes to said upper chamber, and auxiliary pump means for withdrawing liquid from said upper chamber and returning it to said lower chamber.

2. Apparatus as claimed in' claim 1; said'passage comprising a tubular member extending upwardly in said upper chamber with apertures adjacent its upper end and with its lower end cornmunicating with the upper end of said lower chamber, and means controlled by movement of said plunger for by-passing liquid from beneath the plunger to said upper end of the lower chamber when the liquid accumulating beneath said plunger reaches said particular magnitude.

3. Apparatus as claimed in claim 1, said passage comprising a tubular member extending upwardly in said upper chamber with apertures adjacent its upper end, and with its lower end communicating with the upper end of said lower chamber, and means controlled by movement of said plunger for by-passing liquid from beneath the plunger to said upper end of the lower chamber when the liquid accumulating beneath said plunger reaches said particular magnitude, said plunger having a rod extending through said -passage and the upper end of said rod projecting out of said upper chamber and indicating the Volume of accumulated liquid beneath the plunger.

4. Apparatus as claimed in claim l, said passage being in communication with the upper end of said lower chamber and said plunger comprising a normally closed valve adapted to be opened when said plunger reaches a particular elevation, thereby by-passing liquid through the plunger to said upper end of the lower chamber.

5. Apparatus as claim in claim l, said passage comprising a tubular member extending upwardly through said upper chamber with apertures adjacent its upper end and with its lower end in communication with the upper end of said lower chamber, said plunger having a rod eX- tending through said tubular member and a normally closed valve adapted to be opened when said plunger reaches a particular elevation. thereby by-passing liquid through the plunger to said upper end of the lower chamber, the upper end of said rod projecting out of said upper chamber and indicating the Volume of accumu- 4 lated liquid beneath the plunger. 

